KENTWOOD, La. - As the long, wet slog that was Hurricane Isaac slouched off into Arkansas, weary residents of Louisiana and Mississippi confronted the muddy, powerless - and dangerous - mess left behind.

Nearly 2 feet of rain fell on the states, leaving the ground too soaked to absorb the overflowing rivers and pushing dams and levees outside New Orleans to the brink. As the water swallowed cars, houses and roads, helicopters and boats swept in to pluck families and pets from rooftops.

At least four deaths were reported in Louisiana and Mississippi. The latest two victims, a man and a woman, were discovered late Thursday in a home in the hard-hit town of Braithwaite, south of New Orleans. Their names were not immediately released.

National Hurricane Center Director Rick Knabb said the storm surge and unrelenting rain will pose "significant and ongoing" hazards.

"For some folks in Arkansas, the event is just beginning," he said. "Flooding is a risk over widespread areas."

Isaac, downgraded Thursday to a tropical depression, will move over Arkansas today and southern Missouri tonight and Saturday, before moving into Illinois on Sunday.

The storm knocked out power to almost a million households and businesses in Louisiana and 150,000 in Mississippi. Airline, rail and highway travel was expected to be snarled through week's end.

Disaster modeler Eqecat estimates Isaac did $2.5 billion in damage. President Obama has declared both states disaster areas.

"I realize in a large sense that Katrina was worse, but this one's doing a lot of damage in small areas. The areas that are getting hit are getting hit hard," said Dorothy Lewis, 58, who evacuated her Kentwood home in Tangipahoa Parish, a mile from the swollen Tangipahoa River.

A few miles north near the Mississippi-Louisiana border, engineers started a controlled release of water Thursday afternoon to reduce the threat of a break at the earthen Percy Quin Dam. If the dam failed, it could send a devastating rush of water that would raise the Tangipahoa 17 feet and wash out hundreds of homes along its banks, including Lewis'.

Louisiana Gov. Bobby Jindal called the situation "the biggest challenge" facing the state Thursday and said 40,000 to 60,000 people would be affected if the dam breaks. Search-and-rescue teams evacuated residents within a 1-mile area .

"It's so stressful," said Pat Womack, who rode out Isaac's lashing in a local church and then returned home only to evacuate again - this time to her brother-in-law's powerless house - to wait for the river to recede. "You don't know what's going to happen. I hope it ends soon."

The $14.45-billion hurricane-protection system ringing the New Orleans area, installed after Katrina's catastrophic levee breaches, continued to hold, keeping storm surge and floodwaters out of the city - but in suburbs and small towns nearby, the situation was dire:

•In LaPlace, the National Guard evacuated 3,000 people trapped by flooding. One couple used a flashlight to signal a Coast Guard helicopter rescue crew, which plucked them and their two dogs from a flooded home early Thursday, said Lt. Cmdr. Jorge Porto, an Air Station New Orleans pilot.

The floods "were shockingly fast-rising," Lt. Gov. Jay Dardenne said.

As the water receded and the rain let up, residents returned to the River Forest community to retrieve soaked belongings or check on their homes. With water too high to drive, many came by boat or waded barefoot through waist-high water.

"I'm fine,'' said Wayne Jones as he waded shirtless. "But I don't know where my family is.''

•In Plaquemines Parish, where 8-foot-high tidal levees keep storm water and high tides at bay, a storm surge leapt over the barriers and overran the fishing enclave of Braithwaite, said Bob Turner, regional director of the Southeast Louisiana Flood Protection Authority-East.

State and parish officials began the days-long process Thursday to release the trapped floodwater by punching a hole in a levee north of Braithwaite and letting it drain into marshes , Turner said.

Alice Sino's Braithwaite home is on the wrong side of the massive floodgate that protects New Orleans. When Isaac bore down, she and her husband fled a day before the floodwaters overwhelmed her home. Sino remembers when workers raised the floodgate near her home. She took it as a bad sign. "When they put it up, I said, 'They're going to drown us out,'" Sino said. "And that's exactly what happened."

•In Slidell, David and Gina Oliver were sitting on their front porch on Wednesday afternoon when they saw the water climbing up to their yard. "Thirty minutes later, the house was full," Gina Oliver said.

The couple evacuated with their two children to her mother's house farther inland. But they were back Thursday afternoon, loading their small fishing boat onto a flooded road to get back to their house and salvage anything they can.

"I don't wish bad on anyone, but they fixed New Orleans. They're high and dry," Gina Oliver said. "And still, all you hear is New Orleans, New Orleans, New Orleans. You haven't heard a damned thing about Slidell."

Richard Roussell, 45, a construction worker in Slidell, walked along the train tracks on Front Street after checking on a house he had finished renovating just two weeks ago.

"I thought it was a little baby storm, but obviously I was wrong," he said. His home had about a foot of water inside. "It ain't pretty."